Browser engines process the instructions on Web pages written in HTML, JavaScript, and CSS, rendering the page on a person’s smartphone, tablet, or computer. WebKit is used in Apple’s Safari, Google’s Chrome, and the unbranded Android browser. With Opera’s change, there will be three major browser engines remaining: WebKit; Microsoft’s Trident, used in Internet Explorer; and Mozilla’s Gecko, used in Firefox and Firefox OS. Opera will move most of its its mobile and PC browser software to WebKit gradually this year, starting with an Android version that will debut at Mobile World Congress this month.

The concern about Opera’s WebKit move stems from the way new features are added to the Web. Typically new ideas appear in one browser or another, then spread to formal standardization efforts that rely on multiple independent browsers implementing those features. With Opera moving to WebKit, there’s one less independent voice about the best way to approach new features.

“Opera’s political power in the Web standards community will take a serious blow,” browser compatibility expert Peter-Paul Koch said in a blog post:

Remember: in order to become a standard, any innovation in Web technologies must have at least two interoperable implementations. That used to mean two out of four; now it means two out of three. Will Opera’s move actually decrease the speed of innovation?

Sure, they can add a feature to WebKit, but that’s not the same as adding it to Presto and shipping it. There’s rather a lot of players involved in WebKit, and some may disagree with the proposed standard and not implement it.

O’Callahan fears the same outcome: “Their impact on Web standards will be dramatically reduced, especially where they want to do something differently to Apple and Google,” he said.

On the flip side, perhaps the most articulate explanation for the move came from Bruce Lawson, Opera’s Web evangelist who has worked on Opera’s standards support for more than four years:

Opera’s Presto engine was a means to an end; a means for a small, European browser company to challenge the dominance of companies who, at that time, hoped to “win” the web through embracing, extending and extinguishing Web standards.

Presto showed that it was possible to make a better browser while supporting standards. Other vendors have followed this path; the world has changed.

These days, Web standards aren’t a differentiator between browsers. Excellent standards support is a given in modern browsers. Attempting to compete on standards support is like opening a restaurant and putting a sign in the window saying “All our chefs wash their hands before handling food.”

…It seems to me that WebKit simply isn’t the same as the competitors against which we fought, and its level of standards support and pace of development match those that Opera aspires to.

Another who called the worries overblown is JavaScript guru John Resig.

“Don’t worry that ‘everyone moving to WebKit causes stagnation.’ Apple created WebKit, Google made it awesome. Opera will make it better!” Resig tweeted.

But Web developer and author Francois Remy said that Resig was missing the point. “We don’t fear stagnation, we fear that WebKit source code becomes the Web documentation and that WebKit bugs becomes the standards,” he said. “If WebKit becomes de facto, we’re up for IE6 all over again,” he added.

Internet Explorer 6 dominated Web usage for years last decade, and it’s only gradually fading from the market despite concerted efforts by Microsoft and just about everybody else in the Web community. Although it was a competitive browser when it arrived, it languished for years, and rivals such as Mozilla had to work hard to try to encourage programmers to support industry standards rather than treat IE as the standard.

Resig, though, said it’s a moot point: “I don’t see this argument as being relevant anymore. WebKit is already a de facto standard. I mean, everyone remembers when the browsers decided to implement -webkit vendor prefixes? It’s obvious that the ‘WebKit is an de facto standard’ horse has already left the gate.”

In Web development, programmers use prefixes when they want to invoke a feature that’s available only in a particular browser that supports it. Developers writing mobile versions of Web sites, though, sometimes used only a “-webkit” prefix even when Mozilla, Opera, or IE also supported that feature, because WebKit is so dominant in mobile browsing. As a result, Opera and Mozilla decided to implement -webkit prefixes even though they’re not WebKit browsers.

Even with an independent browser engine, though, Presto wasn’t effective, argued one Opera quality-assurance employee in a blog post.

“Yes, monoculture is bad, but Opera was never really in a position to prevent it in the first place,” he said. “Even with Opera as the dominant mobile browser and more than 300 million active Opera users in total across all platforms, Web developers still designed just for WebKit.”